Circuits, such as regulators or converters, receive power to power active components of the circuit. At start up, when the power is initially applied to the circuit, direct or immediate application of the power at a specified level may cause a power surge, which may damage components of the circuit and cause overshoot of a desired output voltage. To avoid these undesirable effects, a “soft-start” voltage that gradually rises to the specified level may be generated and applied to the circuit.
Some soft-start voltages may be analog, in which a current source may charge a capacitor, producing a relatively smooth and continuous soft-start voltage that increases to a specified or maximum level. The waveform of the analog soft-start voltage may be desirable or ideal due to its smooth and continuous shape. However, a large-sized capacitor is often required to produce the analog soft-start voltage. Due to its large size, the capacitor may be a component that is placed “off chip” or is located external to the circuit, which may increase the overall circuitry in both size and cost.
To generate a soft-start voltage “on chip” or internal to the circuit, the soft-start voltage may be generated as a digital soft-start voltage rather than as an analog soft-start voltage. The digital soft-start voltage may be generated using smaller-sized circuit components that may be integrated “on chip” or internal to the circuit. A conventional digital soft-soft start voltage may have a staircase waveform, which “steps up” in voltage over multiple time intervals. The staircase waveform of the digital soft-start voltage may be relatively discontinuous compared to the relatively smooth, continuous waveform of the analog soft-start voltage. Although generated internal to the circuit, the discontinuous waveform of the digital soft-start signal may be problematic. For example, the staircase waveform may cause an overshoot in the output voltage or some other problem or glitch in the circuit during start up. As such, it may be desirable to generate a digital soft-start voltage that has a smoother waveform similar to the waveform of an analog soft-start voltage, but that is generated using on-chip components.